SCOTT MALONE AND ELLEN WULFHORST

US ATTORNEY general Eric Holder touched down in Ferguson, Missouri yesterday, hours after nearly 50 protesters were arrested on the 11th night of demonstrations over the killing of an unarmed black teenager by a white police officer.

Meanwhile, the St Louis County prosecutor’s office also began presenting evidence to a grand jury investigating the 9 August shooting of Michael Brown, 18.

Prosecuting attorney Bob ­McCulloch said his office could continue presenting evidence to the grand jury until mid-­October as he manages conflicting pressures for speed and thoroughness.

He said: “On one side, people are saying you’re rushing to justice, and on the other side, they’re saying you’re dragging this thing out.

“We’re going to present this as expeditiously as possible, but we are not going to present it in a half-hearted manner.”

Outside Mr McCulloch’s ­office, a few dozen protesters called for him to be removed from the case and for the ­immediate ­arrest of the officer involved in the shooting.

The officer, Darren Wilson, 28, has been placed on leave.

“The criminal justice system in America is as racist as it was 50 years ago,” said African-American minister Stanton Holliday, 62, who said he was a long-time civil rights activist. He added that he was concerned that prosecutors were taking too long.

Mr Holder said he would be briefed on the progress of a separate civil rights investigation he has ordered into the Brown killing.

In Ferguson, some said they hoped Mr Holder’s visit would lead to a swift arrest and prosecution of the police officer involved in the shooting, while others cautioned against hasty justice.

Jason Schmidt, a 28-year-old black man who works for a temp agency, said he hoped the federal government’s involvement would lead to “the killer paying for his actions. If this was done to any other race, to any other place, in any other situation, I don’t think it would have taken this long to get ­justice.”

Another resident, pensioner and Vietnam War veteran Walter Garrett, 66, also black, called for patience. He said: “You don’t want to rush it and have him get off if it turns out he is guilty.”

In a message to the community published online by local newspaper the St Louis Post-­Dispatch, Mr Holder said about 40 FBI agents have been assigned to the case, along with prosecutors in the US attorney’s office in St Louis.

Hundreds of people have already been interviewed, Mr Holder said, and federal medical examiners have performed an independent post-mortem ­examination, the third conducted in the killing.

“Our investigation into this matter will be full, it will be fair, and it will be independent,” Mr Holder said.

He joined state governor Jay Nixon and other officials in a renewed appeal for public calm following demonstrations that have gripped Ferguson since Brown was killed.

Most of the protests have been punctuated by looting, vandalism and clashes between demonstrators and police.

The turmoil has exposed simmering racial tensions in Ferguson, whose police force, political leadership and public education administration are dominated by whites.